Re: [go-nuts] C.malloc of Go type?

[andrey mirtchovski]

also useful if you're dealing with blobs of C memory:

https://utcc.utoronto.ca/~cks/space/blog/programming/GoCGoCompatibleStructs

On Sat, May 19, 2018 at 3:03 PM, Jan Mercl <0xj...@gmail.com> wrote:

>
> On Sat, May 19, 2018 at 10:42 PM Max 
> wrote:
>
> > The question is: is it allowed to take the unsafe.Pointer returned by
> C.malloc() and convert it to a pointer to a Go struct type?
>
> See https://golang.org/pkg/unsafe/#Pointer
> --
>
> -j
>
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Re: [go-nuts] C.malloc of Go type?

[Jan Mercl]

On Sat, May 19, 2018 at 10:42 PM Max 
wrote:

> The question is: is it allowed to take the unsafe.Pointer returned by
C.malloc() and convert it to a pointer to a Go struct type?

See https://golang.org/pkg/unsafe/#Pointer
-- 

-j

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[go-nuts] C.malloc of Go type?

[Max]

After reading https://golang.org/cmd/cgo/#hdr-Passing_pointers and 
https://blog.golang.org/c-go-cgo,
I am trying to understand if there are valid ways to pass between Go and C 
complicated data structures
with (potentially) lots of pointers.

At the moment this is just a speculative question, but it could quickly 
become useful both for my Go interpreter gomacro
and for other similar tasks (I am thinking at least about 
https://github.com/gijit/gi) that need to pass arbitrary
data structures between compiled Go code and the interpreter itself (which 
may not be written in Go).

The question is: is it allowed to take the unsafe.Pointer returned by 
C.malloc() and convert it to a pointer to a Go struct type?

In practice: is the following code valid ?

Thanks,

Max

// 
-

package main

/*
#include 
*/
import "C"

import (
"fmt"
"unsafe"
)

type List struct {
Node int
Next *List
}

func mallocList() *List {
const n = unsafe.Sizeof(List{})
p := C.malloc(C.ulong(n))
C.memset(p, C.int(n), 0)
return (*List)(p)
}

func main() {
// if this code is valid, x can contain C pointers and can be passed 
freely to C code,
// thus exchanging complicated data structured between Go and C

x := mallocList()
x.Next = mallocList()

fmt.Printf("%#v\n", x)
fmt.Printf("%#v\n", x.Next)
}

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